WASHINGTON (Reuters) – A U.S. congressman who is leaving the Republican Party said on Sunday that President Donald Trump’s personal attacks against critics intimidate others in the party from speaking out against him, but said, “It doesn’t scare me.”

Representative Justin Amash, who quit the party here last week, told CNN that Republican lawmakers fear being singled out by fellow Republican Trump for personal, nasty attacks and that keeps them silent about Trump’s conduct.

“It’s a big part of it. They’re afraid they’ll be attacked,” Amash said on CNN’s State of the Union program.

Amash’s decision to speak out about Trump after U.S. Special Counsel Robert Mueller’s report in May on Russian interference in the 2016 presidential election drew the president’s fury and a prompt Republican primary challenge for the district in Michigan that he has represented since 2011.

Amash, 39, said the Mueller report showed Trump had obstructed justice, bucking his party and echoing the conclusions of many Democrats, whose caucus is divided about whether to begin impeachment proceedings in the U.S. House of Representatives.

Trump denies any wrongdoing.

Amash told CNN he is running in Michigan for reelection to Congress as an independent. Asked about possibly running for president as an independent or libertarian, Amash said, “I still wouldn’t rule anything like that out.”

Trump officially began his re-election campaign on June 18 and more than 20 Democrats are campaigning for their party’s nomination to run against Trump in 2020.

When Amash said he was leaving the party, Trump tweeted, “Great news for the Republican Party as one of the dumbest & most disloyal men in Congress is ‘quitting’ the Party.”

Trump also took to Twitter to attack Amash in May after his comments that Trump committed impeachable offenses.

Trump said Amash was “a total lightweight” and “a loser.”

On Sunday, Amash said that “most people understand that’s not how people are supposed to talk about each other and to each other.”

He said Trump “thinks people owe loyalty to him. But people are elected to Congress with an oath to support and defend the Constitution, not an oath to support and defend one person.”

On attacks against him by Trump and Trump’s family, he said, “It doesn’t scare me … What the president is doing is actually lowering the tone across the country … A lot of people put up with it because the economy is good right now. But I don’t think they put up with it if things went south.”

Amash said House Speaker Nancy Pelosi is mistaken in holding off fellow Democrats from pursuing impeachment proceedings.

“From a principled, moral position, she is making a mistake,” he said. “If she believes, as I do, that there is impeachable conduct … Then she should say so.”